Which drugs are associated with highest risk for being arrested for driving under the influence? A case-control study.

The aim of this study was to determine the association between drug type and arrest for driving under the influence of drugs (DUID) by calculating odds ratios (ORs) using a case-control design. A DUID arrest is in most cases related to aberrant or risky driving and might therefore be regarded as a proxy for a drug related traffic crash. The 'cases' were 2738 drivers arrested on suspicion of drugged driving from April 2008 to March 2009 with blood alcohol concentrations below the legal limit of 0.2g/L; 794 were arrested due to involvement in road traffic crashes, whereas 1944 were arrested for other reasons, mainly dangerous driving, suspected impairment when stopped in traffic controls, or because of phone calls to the police from other road users or observers. The 'controls' were 9375 random drivers in normal traffic, also with alcohol concentrations below this limit. Blood samples from 'cases' and oral fluid samples from 'controls' were analyzed for 15 drugs that have legislative concentration limits in Norway, in addition to two other commonly detected psychoactive drugs. The most prevalent illicit drug in the control group was tetrahydrocannabinol (THC; 0.58%), which was also commonly found in samples from drivers arrested due to road crash (15.6%) or arrested for other reasons (21.8%). Amphetamine/methamphetamine was most prevalent among arrested drivers involved in crashes (30.6%) and drivers arrested for other reasons (56.9%), whereas only 0.18% of the control group was positive for amphetamine/methamphetamine. The single-use substances which gave highest OR for police arrest were amphetamine/methamphetamine, alprazolam, clonazepam and oxazepam. The majority of the alprazolam and clonazepam findings were probably due to non-therapeutic use of medicinal drugs purchased on the illegal market. Combinations of two or more drugs yielded higher ORs than the use of single substances; combinations of amphetamine/methamphetamine and benzodiazepines gave the highest risk.